FAIRFIELD COUNTY, Conn. -- A recent study by the Regional Plan Association held an ominous message for Fairfield County commuters frustrated with the performance of Metro-North: It could be a long time before things get better on the commuter railroad.

It could take up to two decades for the New Haven Line to be restored to full operating capacity at the current rate of investment from Connecticut and New York, RPA's study said.

The study went on to say that $3.6 billion more than what is already being invested in the New Haven Line would be required to fully modernize the 60-mile stretch of railroad that runs through Connecticut into Manhattan.

“The New Haven Line supports the biggest and most diverse economy in the country, yet this crucial piece of infrastructure is no longer up to the task,” RPA President Robert D. Yaro said in a statement. “If we don’t maintain our vital infrastructure, we will be subjecting a generation of commuters and long-distance travelers to relentless, disruptive repair work and jeopardizing the growth and prosperity of our region.”

Expediting upgrades to the railroad would create larger service disruptions in the short term but would allow four-track service to become a reality much sooner, RPA said.

Having all four tracks operational is vital given the anticipated population growth along the corridor accommodating passengers transferring from the region’s branch lines, including from the New Haven-Hartford-Springfield commuter line, which is expected to begin service in 2016, RPA said.

The New Haven Line is already the busiest rail line in the United States, carrying 125,000 passengers a day on Metro-North and Amtrak.

The study's action plan to get the railway up to speed included upgrades to power and signal systems; repairs to tracks and station platforms; and rehabilitation or replacement of the five movable bridges that are a source of continued service disruptions.